| Summary: | 碩士 === 國立臺灣大學 === 植物學研究所 === 90 === Fern rheophytes are fern species which are in nature confined to the beds of swift-running streams and rivers and grow there up to flood-level, but not beyond the reach of regularly occurring flash floods. Stream and river ecosystems are common in Taiwan resulted from the great precipitation of Taiwan. Because of the wet climate suitable for ferns, the abundance and richness of ferns are high in Taiwan. Rheophytic ferns and their habitats were hardly described in Taiwan though there were several researches concerning about the vegetation of single watershed around Taipei or about the population genetic structure of the rheophyte Acorus gramineus in Taiwan. The aim of this study is to analyze the vegetation compositions of different watersheds around low-altitude suburbs in Taipei and to characterize the habitats of fern rheophytes.
Sixty-two 5×5m2 plots were set to investigate the species compositions and their coverages by means of line transect method. The canopy coverage and species were also evaluated and recorded respectively. Substrate types that ferns lived on, the positions and directions that ferns lived on the substrates, and the height that ferns grew above stream water surface were recorded. For three rheophytic fern species, Bolbitis appendiculata, Microsorium pteropus and Lindsaea japonica, the length and width of their fronds were especially measured.
There were 227 understory species belonging to 85 families recorded, and 77 species were ferns. The understory vegetation of watersheds studied can be divided into three types after TWINSPAN and DCA studies. The vegetation types were correlated to altitude, canopy coverage and the width of streams. However, the vegetation types were not correlated to the aspect and northeast monsoon. The obligate rheophytic ferns were different from facultative rheophytic or dry-land ferns by the living positions and directions of them on the substrates and the height range from stream water surface. The habitats of three rheophytic ferns were different from each other by their canopy coverages, substrate types and the height range from stream water surface. But they all tended to live on the position and direction which might suffer the more serious floods. The frond length/width ratios of them were ranging from 3 to 9.
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